1. Field of the Invention
The present invention relates to an image recording apparatus which accesses a memory storing data used in detecting a life of a replaceable cartridge.
2. Related Background Art
Conventionally, an image recording apparatus of an electrostatic photographic system using a process cartridge has been known, and a structure of the apparatus has been described in, e.g., Japanese Patent Application Laid-Open No. 8-160680. The process cartridge is integrally composed of a photosensitive drum, a charger, a development unit, a cleaner and the like, and is detachably mounted on the image recording apparatus. The process cartridge involves a nonvolatile memory unit to store the sum total of rotating times of the photosensitive drum. The contents in the nonvolatile memory unit are used to detect whether or not the life of the photosensitive drum terminates.
As described above, the nonvolatile memory unit is arranged in the vicinity of the charger, the development unit, a transfer roller and the like. Therefore, in a case where an electromagnetic noise is generated from a high voltage power supply unit in an image formation apparatus due to, e.g., a discharge (leak) of high voltage applied to the charger, the electromagnetic noise is superimposed on read and write signals of the nonvolatile memory unit. As a result, there is some fear that the stored contents change.
Therefore, in order to prevent that the electromagnetic noise is superimposed on the read and write signals of the nonvolatile memory unit, it is thought that read and write operations of the nonvolatile memory unit are to be performed only when the image recording apparatus is in a standby state. In other words, it is through that the operations are to be performed only when the high voltage is not applied. However, if doing so, the read and write operations of the nonvolatile memory unit can not be performed when the image recording apparatus continuously performs the image recording. For this reason, if such a condition as the read and write operations can not be performed continues for long, the rotating time (period) of the photosensitive drum during this condition is not added to the sum of rotating time (period) previously stored in the nonvolatile memory unit. Thus, if a power supply unit is shut down before the sum of actual rotating time of the photosensitive drum is written into the memory unit, the stored contents are seriously different from the sum of actual rotating time.
Even if the read and write operations of the nonvolatile memory unit are performed while applying of the high voltage in continuous image recording is being stopped, there is some fear that an electric charge transfers onto a paper sheet being moved inside the image recording apparatus and thus discharge occurs on the moving sheet. Due to this discharge, there is some fear that the electromagnetic noise is generated, the generated noise is superimposed on the read and write signals of the nonvolatile memory unit, and thus the data changes by such the superimposed noise.